1. Field of the Invention
The present invention relates to a liquid crystal display apparatus having a plurality of semiconductor chips for driving the liquid crystal display.
2. Description of Related Art
Mounting of a driver IC for driving liquid crystal in a conventional liquid crystal display apparatus will now be described with reference to FIGS. 90, 91, 92 and 93. A driver IC 50041 is mounted on a tape-carrier package (hereinafter referred to as a "TCP") 50042 and connected to a panel 16 while interposing a connection member 19 between the TCP and panel 16. Input lines 50044 and output lines 50045 of the TCP 50042 to and from the driver IC 50041 are disposed on a common surface of the TCP 50042, the connection with the panel 16 being established by using the connection member 19 so that a leading portion 50046 of the output line pattern 50045 on the surface of the TCP substrate 50042 and a panel terminal 18 are connected to each other.
Another method of mounting the driver IC for driving liquid crystal in the conventional liquid crystal display apparatus will now be described with reference to FIGS. 90, 91, 92, 93, 94 and 95. The driver IC 50041 is mounted on the tape-carrier package 50042 and connected to the panel 16 while interposing an anisotropic conductive film 50049 between the TCP and panel 16. In the TCP 50042, the input lines 50044 to the driver IC 50041 and the output lines 50045 from the driver IC 50041 are disposed on the surface of the substrate TCP 50042 and are connected to the panel 16 in such a manner that the leading portion 50046 of the output line pattern 50045 on the surface of the substrate TCP 50042 and the panel terminal 18 are connected using the anisotropic conductive film 50049. The anisotropic conductive film 50049 is mainly made of conductive particles 50050 and an adhesive agent 50051. The thickness (H) of the adhesive agent 50051 is made to be larger than the particle size (D) of the conductive particles 50050. If the thickness (K) of the leading portion 50046 of the TCP 50042 is larger than the particle size (D) of the conductive particle 50050, a connection state shown in FIG. 95 is therefore realized in which the conductive particles 50050 are crushed so that conduction is established. If the thickness (k) of a connection terminal 50046 is smaller than the particle size (D) of the conductive particle 50050, as shown in FIG. 96, the adhesive agent 50051 cannot be displaced sufficiently to cause a reliable electrical connection. In this case, there arises a problem in that the electrical connection by the conductive particles 50050 cannot be established satisfactorily.
The input line 50044 to the driver IC 50041 is, by soldering, connected to another substrate (hereinafter called a "bus substrate") 50043 for supplying input signals and electric power to IC 50041. The bus substrate 50043 is formed into a two-layer shape so that the bus line can be wired in a cross manner. The detailed description about the wired portions and connection portions are omitted here. The major portion of the TCP 50042 and the bus substrate 50043 are positioned outside the outline of the panel 16 causing the area required to mount the semiconductor chip to be very wide. Further, the bus substrate must be used as an individual element and, accordingly, the cost cannot be reduced.
A COG (Chip On Glass) method will now be described with reference to FIG. 93. FIG. 93 is a cross sectional view which illustrates an essential portion in which the semiconductor chip is mounted by the COG method. If a bus line 50048 is intended to be wired on the panel substrate, it must be wired on the panel substrate in a manner crossing an input line 50047 to the driver IC 50041. Since the lines must be formed by thin metal films made of Au or Ni or the like, each line must have a large width in order to reduce its resistance value. Therefore, a large area is required to mount the semiconductor chip, and even worse, the cost cannot be reduced because wiring using the thin metal film must be performed in the cross manner.
A conventional liquid crystal display apparatus includes display pixels defined by a matrix of electrodes formed by line electrodes and column electrodes. Display signals for driving a semiconductor device disposed in the peripheral portion of the liquid crystal display device in a TAB (Tape-Automated-Bonding) manner are supplied to an electrode terminal of the display device, which is connected with an anisotropic conductive adhesive agent or a conductive rubber connector.
FIGS. 97 and 98 illustrate an example of the mounting structure employed in a liquid crystal display apparatus in which a semiconductor device mounted in the TAB manner is connected to a liquid crystal display device.
Referring to FIGS. 97 and 98, a TCP 50151 for driving liquid crystal comprises a semiconductor device 111 for driving liquid crystal which is mounted on a flexible wiring member 50152 in the so-called TAB method. Further, a TCP output terminal 50153 disposed on one side of the TCP 50151 is connected to the terminal portion of a liquid crystal member 110 with an anisotropic conductive agent 115, while a TCP input terminal 50154 and a drive control circuit substrate 50155 disposed on the other side are connected by soldering.
Since the foregoing conventional technology must comprise an individual wiring substrate (the bus substrate) for supplying input signals and electric power to the driver IC and metal thin film lines wired in the cross manner, the area required for mounting the semiconductor chip cannot be reduced. Therefore, there arises a problem in that a liquid crystal display apparatus, the cost and the size of which can be reduced, cannot be provided.
The foregoing conventional technology has an arrangement in which semiconductor devices for driving liquid crystal are, by a TAB mounting method, connected to the electrodes of the liquid crystal display devices in the sequential order of the column (sequentially connected in parallel to the pixels) while being formed into a TCP shape for each semiconductor device. Further, the semiconductor devices are connected to a drive control circuit substrate for supplying electric power for driving liquid crystal and control signals (hereinafter called "bus lines").
Since a liquid crystal display apparatus of the type having the foregoing mounting structure and adapted for color display requires a pixel density three times that of a black and white display apparatus when the same resolution as that realized by the black and white display apparatus is intended to be realized, the number of lines for mutually connecting the TCPs increases excessively, making it difficult if not impossible to maintain reliability in the connections. Further, the drive control circuit substrate must have a precise wiring rule due to the increase in the number of the terminals, and, accordingly, the substrate must be formed into a multi-layer shape. As a result, the size of the liquid crystal display apparatus cannot be reduced and the number of required elements increases undesirably. Therefore, the overall cost of the apparatus cannot be reduced.
FIG. 99 is a view which illustrates the structure of a conventional color liquid crystal display apparatus disclosed in Japanese Patent Laid-Open No. 2-214826. In order to be adaptable to the increased number of the color display pixels, TCPs 50151-1 to 50151-3 are formed into three layers. The portions of the foregoing TCPs 50151-1 to 50151-3 that are connected to the drive control circuit substrate 50155 are arranged in the same manner as those of the structure shown in FIG. 98. Therefore, the number of required connections increases due to the rise in the pixel density. Hence, the defect occurring in the connection cannot be prevented. Even worse, the structure, in which the TCPs are stacked, causes the semiconductor device to project in the direction of the thickness, resulting in a problem in that the size of the apparatus cannot be reduced.